The present invention relates to a method of manufacturing a nonaqueous-gel-electrolyte battery which is capable of generating high voltage and exhibiting great discharge energy.
In recent years batteries have been used as important power sources for portable electronic apparatus. In particular, secondary batteries have been employed as batteries for operating portable electronic apparatuses from a viewpoint of advantages of economic merits and saving of resources. Therefore, purposes of the secondary batteries have rapidly been increased in recent years.
There are requirements for reducing the size and weight of the portable electronic apparatus. Also the portable electronic apparatus does not require a large accommodating space in the apparatus. To prevent enlargement of the overall weight of the electronic apparatus, reduction in the weight of the battery has been required. Moreover, permission of use of the battery for a long time has been required. That is, size reduction and improvement in the performance of the portable electronic apparatus cause the size and weight of the adaptable battery to be reduced and the performance to be improved.
To meet the above-mentioned various requirements, nonaqueous lithium secondary battery has attracted attention because of its higher energy density and output density as compared with those of lead batteries and nickel-cadmium batteries.
The nonaqueous lithium secondary battery is a battery of a type which uses an electrochemical reversible reaction with which lithium contained in the positive electrode is, during a charge operation, occuluded in the negative electrode through the electrolytic solution. During a discharge operation, lithium in the negative electrode is occuluded in the positive electrode through the electrolytic solution. As the electrolytic solution, a nonaqueous solvent prepared by dissolving lithium salt is employed.
To prevent leakage of the electrolytic solution, a metal container having rigidity, that is, a so-called hard cell (a positive electrode cover and a negative electrode can) is employed as the case.
However, the foregoing metal hard cell suffers from a problem in that the hard cell cannot satisfactorily meet the above-mentioned requirements for reducing the weight, size and the thickness. Moreover, raising of a degree of freedom permitted when the shape of the secondary battery is designed has been required because the size of the electronic apparatus has furthermore been reduced. The metal hard cell cannot satisfactorily meet the requirement about the shape. It is very difficult to manufacture, for example, a sheet battery having a small thickness and a large area, a card battery having a small thickness and a small area and a flexible battery having a great degree of freedom.
As an effective means for solving the above-mentioned problems, it might be considered feasible to manufacture a battery incorporating an inorganic or organic and perfect solid electrolyte or a semi-solid electronic apparatus constituted by polymer gel. Specifically, a so-called solid electrolyte battery and a nonaqueous-gel-electrolyte battery (also called a xe2x80x9cpolymer lithium batteryxe2x80x9d or simply called a xe2x80x9cpolymer batteryxe2x80x9d) have been suggested each of which incorporates a polymer and solid electrolyte composed of polymer and an electrolyte or a gel electrolyte prepared by adding nonaqueous electrolyte to matrix polymer as a plasticizer.
The nonaqueous-gel-electrolyte battery has a positive electrode incorporating a positive-electrode collector on which an active material layer of the positive electrode is formed by coating. The negative electrode of the nonaqueous-gel-electrolyte battery has a negative electrode incorporating a negative-electrode collector on which an active material layer of the negative electrode is formed by coating. Moreover, a gel layer containing an electrolyte is held between the active material layer of the positive electrode and the active material layer of the negative electrode.
The gel layer containing the electrolyte of the nonaqueous-gel-electrolyte battery has a structure that the electrolytic solution is held in the gel matrix. It leads to a fact that the nonaqueous-gel-electrolyte battery does not suffer from the leakage of the electrolytic solution. Therefore, the hard cell is not required so that reduction in the size, weight and the thickness and improvement in the degree of freedom are permitted.
The nonaqueous-gel-electrolyte battery, which incorporates the electrolytic solution held in the gel matrix, suffers from a problem in that penetration of the electrolytic solution into the active material layers of the electrode cannot sufficiently be performed. Therefore, lithium ions cannot sufficiently be moved between the two electrodes, thus resulting in a problem to arise in that a required capacity of the battery cannot be realized.
An object of the present invention is to realize a large capacity of a nonaqueous-gel-electrolyte battery, which incorporates an active material layer of a positive electrode and an active material layer of a negative electrode on each of which a gel layer containing electrolytic solution is formed by coating and which has a structure that the gel layers each containing the electrolytic solution are laminated, by facilitating penetration of the electrolytic solution held in the gel matrix of the gel layers each containing the electrolytic solution into the active material layers of the electrodes.
The inventors of the present invention have detected a fact that penetration of the electrolytic solution into the active material layers for the electrodes is facilitated by, in sol state, coating each of the active material layers for the electrodes with the gel layer containing the electrolytic solution. Thus, the present invention has been produced.
According to the present invention, there is provided a method of manufacturing a nonaqueous-gel-electrolyte battery incorporating a positive electrode constituted by forming an active material layer of the positive electrode on a positive-electrode collector; a negative electrode constituted by forming an active material layer of the negative electrode on a negative-electrode collector; a gel electrolyte layer formed by coating the surface of the active material layer of the positive electrode and/or the surface of the active material layer of the negative electrode with a gel electrolyte composition and having a structure that the positive electrode and the negative electrode are laminated to hold the gel electrolyte layer therebetween, the method of manufacturing a nonaqueous-gel-electrolyte battery comprising the step of: forming the gel electrolyte composition into a sol form; and coating the surface of the active material layer of the positive electrode and/or the surface of the active material layer of the negative electrode with the gel electrolyte composition in the form of sol.
It is preferable that the gel electrolyte composition formed into the sol form has viscosity of 1 cp to 50 cp.
To form the gel electrolyte composition into the sol form, the gel electrolyte composition is heated or diluted with nonaqueous solvent. When dilution using the nonaqueous solvent is performed, solvent having a high boiling point and solvent having a low boiling point which are mixed with each other is employed. After the coating process has been completed, the solvent having the low boiling point is removed by vaporization.
It is effective to heat the positive electrode or the negative electrode when coating of the gel electrolyte composition formed into the sol form is performed.
When the active material layer of the positive electrode or the active material layer of the negative electrode is coated with the gel electrolyte composition formed into the sol form, penetration of the gel electrolyte, and in particular, electrolytic solution into the active material layers can be facilitated.